Electrical insulating oil



United States Patent 3,287,259 ELECTRICAL INSULATING OIL Gerald D. Staflin, Westfield, and James E. Kehoe, Clark, NJ., and Carl J. Rizzuti, New York, N.Y., assignors to Esso Research and Engineering Company, a corporation of Delaware No Drawing. Filed Dec. 17, 1963, Ser. No. 331,129 Claims. (Cl. 208264) This invention relates to hydrocarbon oils which are useful as electrical insulating oils and to methods for preparing them. More specifically, this invention relates to hydrocarbon oils which are particularly useful as heavy paper-impregnation type cable oils. In one particular aspect, this invention relates to hydrocarbon oils which are prepared by the multiple hydrofining of aromatic oils.

BACKGROUND Cable oils are designed for use in impregnating the paper wrapping which is wound around electrical cables. Such oil-impregnated papers are also used as the principal insulation for many capacitors and transformers. A major factor in the market acceptance of cable oils is that such oils must possess good electrical properties as determined by power factor and dielectric strength measurements, good oxidation stability, a high viscosity at low temperatures to prevent oil migration in service (bleeding) and a low viscosity at high temperatures to allow for ease in effective impregnation during cable manufacture. This latter feature (i.e., ease in impregnation) is particularly important since oil voids must be substantially or completely eliminated. In addition, such an oil must remain liquid at low ambient temperatures to prevent the subsequent formation of voids in the insulation during service. Minute imperfections can be disastrous. Such an oil must also be adequate in terms of other conventional oil properties such as sulfur content, etc.

DISCOVERY It has now been discovered, and this discovery forms the basis of the present invention, that aromatic oils may be hydrofined in at least two stages to produce an oil useful as an electrical insulating oil. These oils will find particular use as cable oils and are capable of meeting current rigid commercial specifications for such cable oils.

Hydrofining is a conventional petroleum process for treating various hydrocarbon streams and improving or altering their qualities. Usually, oils which are to be hydrofined are napthenic in nature (e.g., see Wasson and Kehoe, US. No. 3,000,807). However, aromatic feed materials (alone or as a component part of a distillate oil) have occasionally been treated by hydrofining. However, even when a highly aromatic oil such as an aromatic extract is subjected to hydrofining under conventional conditions, the resulting product is deficient in many of the properties required of a cable oil. The original aromatic oil (prior to hydrofining) is even more deficient in these properties. The present invention resides in the surprising discovery that anaromatic oil which is deficient in these properties may be hydrofined under conventional conditions, which hydrofined oil is improved, although still deficient in many properties, e.g., deficient in power factor, deficient in dielectric strength, deficient in oxidation stability, etc. This hydrofined aromatic oil is then subjected to at least one more hydrofining operation, also under conventional conditions. The product recovered from the second or final hydrofining operation has been found to possess all of the presently required properties of a cable oil. The resulting product is then a cable oil having very desirable properties, which oil is commercially acceptable.

date on alumina, and'the like.

3 ,287,259 Patented Nov. 22, 1966 FEED STOCKS Ordinarily (and preferably) the feed stocks used for the first hydrofining step will be distillate oils (e.g., coastal distillates) which contain significant amounts of aromatics and which boil within the range of 600 to 1000 F., e.g., 700 to 900 F. After the oil has been hydrofined for the first time, the hydrofined distillate will be extracted to remove the hydrofined aromatic portion therefrom. The hydrofined aromatic portion is then hydrofined at least a second time to produce the desired doubly-hydrofined product. Experience has shown that the aromatic extract, both before and after the second hydrofining step, will boil within substantially the same ranges as cited for the original distillate oils. However, viscosity measurements on these oils do show significant variations. For example, a typical distillate oil boiling within the cited ranges has a viscosity of about 900 SUS at 100 F. The viscosity after hydrofining (the first time) and after phenol extraction is about 6000 SUS at 100 F. After the second hydrofining step, the viscosity of the doubly-hydrofined product is about 5000 SUS at 100 F.

Alternatively, a highly aromatic oil (e.g., extracted from a coastal distillate) boiling within the cited ranges may be used as the initial feed material and hydrofined two or more times in succession to directly produce the inventive products. In another alternative, 2. distillate oil may be hydrofined two or more times and then extracted to recover the desired doubly-hydrofined aromatic oil.

By the term boil as used herein, it is meant that the temperature at which about 5 vol. percent is first distilled off and the temperature at which about vol. percent has been distilled off (distillations corrected to normal atmospheric pressure) will :both fall within the cited temperature range.

Extraction of the aromatic constituents from a hydrocarbon stream (e.g., from distillate oil or hydrofined distillate oil) may be done by any of a number of well known techniques. Such techniques include the use of glycols, furfural, methanol, phenol, nitrobenzene, etc. Phenol extraction is a preferred technique because it is highly effective in removing aromatics (i.e., single ring aromatics as well as condensed ring aromatics, e.g., 2, 3, 4, or more condensed rings). These various extraction techniques are well known in the art and their selection and operation is well within the skill of the routineer (e.g., patents were granted and plants constructed for phenol extraction during the 1930s).

No reasons are known why highly aromatic Oils obtained from any source would not be suitable for use acording to the present invention.

As indicated earlier, however, it is considered most preferable to use an aromatic extract obtained by the phenol extraction of a hydrofined distillate oil as a feed material to the final hydrofined step( s) PROCESS DESCRIPTION The first hydrofining operation used in the present invention will be conducted in a hydrofining zone at temperatures of from 500 to 700 F., e.g., 550 to 650 F. The feed rate will generally be within the range of 0.5 to 3 volumes of feed per volume of catalyst per hour (v./v./hr.), e.g., 0.75 to 1.25 v./v./h r. Two hundred to 1500, e.g., 700 to 1300 s.c.f. per barrel of free hydrogen are used in the hydrofining zone during the hydrofining operation. Pressure is not critical and can be on the order of 500 to 900 p.s.i.g.; e.g., about 750 p.s.i.g. Any suitable hydrofining catalyst can be used such as cobalt molyb- It is preferred to use catalyst of the type known commercially as Harshaw O301P and Harshaw O60l-P sold by the Harshaw Chemical Company, Cleveland, Ohio. The hydrofining operation for both treatments is conventional (as has been previously stated) and involves passing the oil (either an aromatic oil or a distillate oil containing significant amounts of aromatics), diluted with hydrogen, at the indicated feed rate, temperature, and pressure over a fixed bed of the catalyst.

After hydrofining, the hydrofined oil, may, if desired, be distilled (this is not necessary, but may be done) and a cut boiling within the range of from 600 to 1000 F., preferably 700 to 900 F.; e.g., 750 to 870 F., may be obtained. If a distillate oil has been employed as feed to the first hydrofining zone, extraction of the aromatic portion will ordinarily and preferably be accomplished at this point. In such a situation, this intermediate fractionation will not usually be performed. The hydrofined aromatic-containing oil is then hydrofined at least one additional time at temperatures of from 500 to 700 F.; e.g., 550 to 650 F. The temperature, pressure, catalyst, hydrogen volume, and feed rate used in each subsequent hydrofining step may be (and generally are) the same as that used during the first stage. In any event, these conditions will fall within the recited ranges. Two hydrofining steps are ordinarily all that is required to achieve the desired results. Consequently, the usual operation will consist of only two hydrofining steps.

While it is most preferred that the conditions of hydrofining in the first and subsequent stages be substantially the same and that an aromatic-containing distillate oil be used as the feed material to the first hydrofining operation, and that the first hydrofined oil be extracted between the first and second hydrofining steps, it will be realized that many changes may be made in terms of tempera- 4 Example 1 A coastal distillate boiling within the range of 600 to 1000 F., having a viscosity at 100 F. of 910 SUS and an API gravity of 21.6 was hydrofined in a first hydrofining zone at 600 F., 750 p.s.i.g., one v./v. hr. feed rate using a cobalt molybdate catalyst, and 1000 s.c.f. hydrogen/ bbl. of feed. The hydrofined material recovered from the first hydrofining zone was extracted with phenol using conventional techniques. No fractionation was attempted.

The aromatic extract had a viscoity of 5975 SUS at 100 F. and an API gravity of 13. then hydrofined a second time in a hydrofining zone operating at the same conditions as the first hydrofining zone.

The hydrofined aromatic oil obtained from the second hydrofining operation had a specific gravity of 0.972,. a viscosity at 100 F. of 5113 SUS, a viscosity at 210 F. of 95.7 SUS, etc. (see Table I). No further treating of the oil was accomplished.

Example 2 An electrical cable is fabricated using paper impreg-.

TABLE I Doubly Extract from Hydmfined Commercial One Manufac- 1st Hydroturer s Speci- Aromatic Cable Oil fining Extract fication Viscosity:

SUS at 100 F 5, 975 5, 113 2, 083 1 2, 000 SUS at 210 F 97. 95. 74 96. 33 Z 150 Power factor at 100 0., percent 2. 93 0. 18 0. 67 2 0. 5 Oxidation Stability:

Power Factor at 100 C. after heating for 48 hours at 300 F in an open beaker, percent 0. 70 2. 67 2 5. 0 Dielectric Strength, KV/cm 16. 5 47. 1 39.0 1 30 Flash Pt., COO, F 410 460 460 1 455 Total Sulfur, wt. percent 0. 30 0. 12 0. 23 2 0.35 Free and Corr. Sulfur None None None 2 None Conradson Carbon, wt. percent; 0.03 0. 04 0. 14 2 0. 30

Minimum.

Maximum.

tures, pressures, etc., without departing from the spirit and scope of the present invention.

After the second or final hydrofining operation has been completed (if more than two hydrofining operations are used), the multiple-hydrofined aromatic oil may optionally be treated by conventional clay treating (e.g., clay percolation or clay contacting). Clay contacting and percolation are well established petroleum processes and involve decolorizing oils by contacting them with finely divided clays such as fullers earth or bleaching clays. The clays remove impurities from petroleum fractions and increase their oxidation stability. Suitable industrial clays useful in this invention are Bennett-Clark natural clay and Attapulgus clay. For reasons not quite clear yet, it appears that clay percolation gives better results than clay contacting. Preferably, 0.4 to 1.5 pounds/gal. of absorbent clay is contacted with the oil to be treated at a tem- I perature in the range of 250 to 300 F. Clay percolation is carried out at temperatures in the range of 75 to 225 F. using similar amounts of clay.

EXAMPLES The present invention will be more clearly understood by reference to the following specific examples, which inelude a preferred embodiment of the present invention.

From Table I, it can be seen that the aromatic oil which had only been hydrofined a single time was quite deficient in a number of electrical properties, i.e. .very high power factor, low dielectric strength, etc. quent hydrofining of that hydrofined aromatic oil im proved all those deficient qualities without adversely affecting the properties of the singly hydrofined oil which were already acceptable, e.g., viscosity at 210':

F. It is believed that the properties of the doubly-hydrofined aromatic oil are quite unique. Comparison oi the novel doubly-hydrofined oil with a commercially available premium cable oil (Table I) is very favorable,

with the doubly hydrofined oil being equivalent to or better than the commercially available oil in all respects as shown. Further comparison of the doubly hydrofined oil with the commercial specification clearly indicates that such a product is adequate in the recited properties and will favorably meet the stringent requirements as now imposed by industry.

Having described the present invention with a certain degree of particularity, it will be realized that various modifications may be made within the spirit and scope of the invention as hereinafter claimed. The headings used throughout this disclosure are not intended to be limiting, but are provided only as .a convenience to The aromatic extractwas I Subse-.

the reader. The true nature of our invention is indicated by the scope and nature of the appendant claims.

What is claimed is:

1. A process for producing an oil useful as a cable oil which comprises:

(a) catalytically hydrofining an aromatic-containing oil boiling 'from 600 to 1000" F. to produce a hydrofined oil in a first hydrofining zone operating at a temperature of from 500 to 700 F., a pressure of from 500 to 900 p.s.i.g., a feed rate of from 0.5 to 3 volumes of oil per volume of catalyst per hour and in the presence of from 200 to 1500 standard cubic feet of hydrogen per barrel of oil,

(b) withdrawing said hydrofined oil as an efiiuent from said first hydrofining zone and passing at least an aromatic-containing portion of said withdrawn hydrofined oil to a second hydrofining zone,

(-c) catalytically hydrofining said aromatic-containing portion of said withdrawn hydrofined oil in -a second hydrofining zone to produce a major proportion of doubly hydrofined aromatic cable oil having a boiling point within the range between about 600 to 1000 F., said second hydrofining zone operating at a temperature of from 500 to 700 F., a pressure of from 500 to 900 p.s.i.g., a vfeed rate of from 0.5 to 3 volumes of oil per volume of catalyst per hour, and in the presence of from 200 to 1500 cubic feet of hydrogen per barrel of oil, and

(d) recovering subsequent to second hydrofining zone an aromatic cable oil having a boiling point within the range between about 600 and 1000 F.

2. A process as defined in claim 1 wherein said aromatic-containing oil fed to the first hydrofining zone is aromatic extract.

3. A process as defined in claim 1 wherein the aromatic-containing oil fed to the first hydrofining zone is a distillate oil and wherein the aromatics contained therein, are extracted therefrom subsequent to said second hydrofining, said extracted aromatic oils being useful as a cable oil.

4. A process as defined in claim 1 wherein said aromatic-containing oil fed to the first hydrofining zone is a distillate oil, and wherein aromatic constituents contained therein are removed from the eflluent of said first hydrofining zone by extraction, and wherein said extracted aromatic constituents are fed to said second hydrofiinin g zone.

5. A process as defined in claim 1 wherein said aromatic-containing oil is clay treated subsequent to said second hydrofining and prior to said recovery, said clay treating being accomplished by treating said oil with from 0.4 to 1.5 lbs/gal. of absorbent clay.

6. A process for producing an oil usefiul as a cable oil which comprises:

(a) catalytically hydrofining an aromatic-containing .distillate oil boiling from 700 to 900 F. to produce a hydrofined oil in a first hydrofining zone operating at a temperature of from 550 to 650 F., a pressure of vfrom 500 to 900 p.s.i.g., a feed rate of from 0.5 to 3 volumes of oil per volume of catalyst per hour and in the presence of from 200 to 1500 standard cubic feet of hydrogen per barrel of oil,

(b) withdrawing said hydrofined oil as an effiuent from said first hydrofining zone and extracting said withdrawn hydrofined oil with a solvent to produce a hydrofined aromatic extract,

(c) passing said hydrofined aromatic extract to a second hydrofining zone,

(d) catalytically hydrofining said hydrofined aromatic extract in a second hydrofining zone to produce a major proportion of aromatic cable oil having a boiling point within the range between about 700 and 900 F., said second hydrofining zone operating at a temperature of from 550 to 650 F., a pressure of vfrom 500 to 900 p.s.i. g., a [feed rate of from 0.5 to 3 volumes of oil per volume of catalyst per hour and in the presence of from 200 to 1500 standard cubic feet of hydrogen per barrel of oil, and

(e) recovering a doubly hydrofined aromatic cable oil having a boiling point within the range of between about 700 and 900 F.

7. A process as defined in claim 6 wherein firom 700 to 1300 standard cubic feet of hydrogen are used per 'barrel of oil in each hydrofining zone.

8. A process as defined in claim 7 wherein the feed rate in each hydrofining zone is from 0.75 to 1.25 v./v./hr.

9. A process as defined in claim 8 wherein the solvent is phenol.

10. A process as \defined in claim 9 wherein all hydrofining zones are operated at substantially the same conditions.

References Cited by the Examiner UNITED STATES PATENTS 2,731,506 1/1956 Love et al 260674 2,799,627 7/1957 Haensel 208-96 2,911,354 11/1959 Holder et a1 208-211 3,062,912 11/ 1962 Kelk 174120 3,077,514 2/ 1963 Kan'g 174120 3,112,259 11/ 1963 Grawitz 208-264 3,175,970 3/ 1965 Bercik et al. 208-264 3,190,830 6/ 1965 Rowland et al. 208143 3,192,153 6/ 1965 Smilski 208-2 64 DELBERT E. GANTZ, Primary Examiner.

S. P. I ONES, Assistant Examiner. 

1. A PROCESS FOR PRODUCING AN OIL USEFUL AS A CABLE OIL WHICH COMPRISES: (A) CATALUST HYDROFINING AN AROMATIC-CONTAINING OIL BOILING FROM 600* TO 1000*F. TO PRODUCE A HYDROFINED OIL IN A FIRST HYDROFINING ZONE OPERATING AT A TEMPERATURE OF FROM 500* TO 700*F., A PRESSURE OF FROM 500 TO 900 P.S.I.G., A FEED RATE OF FROM 0.5 TO 3 VOLUMES OF OIL PER VOLUME OF CATALYST PER HOUR AND IN THE PRESENCE OF FROM 200 TO 1500 STANDARD CUBIC FEET OF HYDROGEN PER BARREL OF OIL, (B) WITHDRAWING SAID HYDROFINED OIL AS AN EFFLUENT FROM SAID FIRST HYDROFINING ZONE AND PASSING AT LEAST AN AROMATIC-CONTAINING PORTION OF SAID WITHDRAWN HYDROFINED OIL TO A SECOND HYDRAFINING ZONE, (C) CATALYSTICALLY HYDROFINING SAID AROMATIC-CONTAINING PORTION OF SAID WITHDRAWN HYDROFINED OIL IN A SECOND HYDROFINING ZONE TO PRODUCE A MAJOR PROPORTION OF DOUBLY HYDROFINED AROMATIC CABLE OIL HAVING A BOILING POINT WITHIN THE RANGE BETWEEN ABOUT 600* TO 1000*F., SAID SECOND HYDROFINING ZONE OPERATING AT A TEMPERATURE OF FROM 500* TO 700*F., A PRESSURE OF FROM 500 TO 900 P.S.I.G., A FEED RATE OF FROM 0.5 TO 3 VOLUMES OF OIL PER VOLUME OF CATALYST PER HOUR, AND IN THE PRESENCE OF FROM 200 TO 1500 CUBIC FEET OF HYDROGEN PER BARREL OF OIL, AND (D) RECOVERING SUBSEQUENT TO SECOND HYDROFINING ZONE AN AROMATIC CABLE OIL HAVING A BOILING POINT WITHIN THE RANGE BETWEEN ABOUT 600* AND 1000*F. 